No, not all popcorn ceilings have asbestos, but a vast majority do. The Environmental Protection Agency (EPA) banned its use in 1973, although it still may have been used up through the early ‘90s. But, in general, homes built or remodeled before the early ‘80s likely utilized materials with asbestos. That being said, a professional test is the only way to determine for sure.

Asbestos-containing materials are not easily affected by water and do not disintegrate or dissolve when exposed to it. However, porous materials can deteriorate due to water exposure, leading to the release of asbestos fibers into the air. The settling of asbestos fibers can also occur as water makes them heavy, which reduces the risk of airborne exposure, though future disturbance of the materials could cause risk. Wetting asbestos-containing materials does not constitute safe removal, and the proper handling and disposal of asbestos materials should be left to professionals.

Knob and tube wiring is an older type of electrical wiring that's no longer used and generally not considered safe. However, some homes still have it, or may have a knob and tube wiring system that was incorrectly modified or rigged to work with a modern electrical system. Knob and tube wiring may contain asbestos insulation, but the only way to know is to have the material professionally tested.

Asbestos is a carcinogen, meaning it increases the risk of cancer. Inhaling asbestos fibers is linked to several respiratory issues, including asbestosis, or scarring on the lungs, lung cancer, and mesothelioma, another type of cancer. There's also a link between asbestos exposure and an increased risk of colon cancer and other cancers of the digestive system.

Usually, the people most at risk for disease related to asbestos exposure are those who spend a lot of time working around the material without protection. Electricians who work with asbestos wire have a higher risk of developing mesothelioma or lung cancer due to their exposure.